# Sort (Unix)

In computing, sort is a standard command line program of Unix and Unix-like operating systems, that prints the lines of its input or concatenation of all files listed in its argument list in sorted order. Sorting is done based on one or more sort keys extracted from each line of input. By default, the entire input is taken as sort key. Blank space is the default field separator. The command supports a number of command-line options that can vary by implementation. For instance the "-r" flag will reverse the sort order.

## History

A sort command that invokes a general sort facility was first implemented within Multics. Later, it appeared in Version 1 Unix. This version was originally written by Ken Thompson at AT&T Bell Laboratories. By Version 4 Thompson had modified it to use pipes, but sort retained an option to name the output file because it was used to sort a file in place. In Version 5, Thompson invented "-" to represent standard input.
The version of sort bundled in GNU coreutils was written by Mike Haertel and Paul Eggert. This implementation employs the merge sort algorithm.
Similar commands are available on many other operating systems, for example a sort command is part of ASCII's MSX-DOS2 Tools for MSX-DOS version 2.
The sort command has also been ported to the IBM i operating system.

## Syntax

With no FILE, or when FILE is -, the command reads from standard input.

### Parameters

| Name | Description | Unix | Plan 9 | Inferno | FreeBSD | Linux | MSX-DOS | IBM i |
| -b, --ignore-leading-blanks | Ignores leading blanks. | Yes | Yes | No | Yes | Yes | No | Yes |
| -c | Check that input file is sorted. | No | Yes | No | Yes | Yes | No | Yes |
| -C | Like -c, but does not report the first bad line. | No | No | No | Yes | Yes | No | No |
| -d, --dictionary-order | Considers only blanks and alphanumeric characters. | Yes | Yes | No | Yes | Yes | No | Yes |
| -f, --ignore-case | Fold lower case to upper case characters. | Yes | Yes | No | Yes | Yes | No | Yes |
| -g, --general-numeric-sort, --sort=general-numeric | Compares according to general numerical value. | Yes | Yes | No | Yes | Yes | No | No |
| -h, --human-numeric-sort, --sort=human-numeric | Compare human readable numbers (e.g., 2K 1G). | Yes | No | No | Yes | Yes | No | No |
| -i, --ignore-nonprinting | Considers only printable characters. | Yes | Yes | No | Yes | Yes | No | Yes |
| -k, --key=POS1[,POS2] | Start a key at POS1 (origin 1), end it at POS2 (default end of line) | No | No | No | Yes | Yes | No | No |
| -m | Merge only; input files are assumed to be presorted. | No | Yes | No | Yes | Yes | No | Yes |
| -M, --month-sort, --sort=month | Compares (unknown) < 'JAN' < ... < 'DEC'. | Yes | Yes | No | Yes | Yes | No | No |
| -n, --numeric-sort, --sort=numeric | Compares according to string numerical value. | Yes | Yes | Yes | Yes | Yes | No | Yes |
| -o OUTPUT | Uses OUTPUT file instead of standard output. | No | Yes | No | Yes | Yes | No | Yes |
| -r, --reverse | Reverses the result of comparisons. | Yes | Yes | Yes | Yes | Yes | No | Yes |
| -R, --random-sort, --sort=random | Shuffles, but groups identical keys. See also: shuf | Yes | No | No | Yes | Yes | No | No |
| -s | Stabilizes sort by disabling last-resort comparison. | No | No | No | Yes | Yes | No | No |
| -S size, --buffer-size=size | Use size for the maximum size of the memory buffer. | No | No | No | Yes | No | No | No |
| -tx | 'Tab character' separating fields is x. | No | Yes | No | No | Yes | No | Yes |
| -t char, --field-separator=char | Uses char instead of non-blank to blank transition. | No | No | No | Yes | Yes | No | No |
| -T dir, --temporary-directory=dir | Uses dir for temporaries. | No | Yes | No | Yes | Yes | No | No |
| -u, --unique | Unique processing to suppress all but one in each set of lines having equal keys. | No | Yes | No | Yes | Yes | No | Yes |
| -V, --version-sort | Natural sort of (version) numbers within text | No | No | No | Yes | Yes | No | No |
| -w | Like -i, but ignore only tabs and spaces. | No | Yes | No | No | No | No | No |
| -z, --zero-terminated | End lines with 0 byte, not newline | No | No | No | Yes | Yes | No | No |
| --help | Display help and exit | No | No | No | Yes | Yes | No | No |
| --version | Output version information and exit | No | No | No | Yes | Yes | No | No |
| /R | Reverses the result of comparisons. | No | No | No | No | No | Yes | No |
| /S | Specify the number of digits to determine how many digits of each line should be judged. | No | No | No | No | No | Yes | No |
| /A | Sort by ASCII code. | No | No | No | No | No | Yes | No |
| /H | Include hidden files when using wild cards. | No | No | No | No | No | Yes | No |

## Examples
### Sort by number

The -n option makes the program sort according to numerical value. The du command produces output that starts with a number, the file size, so its output can be piped to sort to produce a list of files sorted by (ascending) file size:
The find command with the ls option prints file sizes in the 7th field, so a list of the LaTeX files sorted by file size is produced by:

### Columns or fields

Use the -k option to sort on a certain column. For example, use "-k 2" to sort on the second column. In old versions of sort, the +1 option made the program sort on the second column of data (+2 for the third, etc.). This usage is deprecated.

### Sort on multiple fields

The -k m,n option lets you sort on a key that is potentially composed of multiple fields (start at column m, end at column n):
Here the first sort is done using column 2. -k2,2n specifies sorting on the key starting and ending with column 2, and sorting numerically. If -k2 is used instead, the sort key would begin at column 2 and extend to the end of the line, spanning all the fields in between. -k1,1 dictates breaking ties using the value in column 1, sorting alphabetically by default. Note that bob, and chad have the same quota and are sorted alphabetically in the final output.

### Sorting a tab delimited file

Sorting a file with tab separated values requires a tab character to be specified as the column delimiter. This illustration uses the shell's dollar-quote notation to specify the tab as a C escape sequence.

### Sort in reverse

The -r option just reverses the order of the sort:

### Sort in random

The GNU implementation has a -R --random-sort option based on hashing; this is not a full random shuffle because it will sort identical lines together. A true random sort is provided by the Unix utility shuf.

### Sort by version

The GNU implementation has a -V --version-sort option which is a natural sort of (version) numbers within text. Two text strings that are to be compared are split into blocks of letters and blocks of digits. Blocks of letters are compared alpha-numerically, and blocks of digits are compared numerically (i.e., skipping leading zeros, more digits means larger, otherwise the leftmost digits that differ determine the result). Blocks are compared left-to-right and the first non-equal block in that loop decides which text is larger. This happens to work for IP addresses, Debian package version strings and similar tasks where numbers of variable length are embedded in strings.